Acyclovir (UK Patent Specification No. 1523865; U.S. Pat. No. 4,199,574) is a compound which has been found to have potent activity against viruses of the herpes family, particularly herpes simplex and herpes varicella zoster. Such activity has been demonstrated by the outstanding success of acyclovir in the therapeutic treatment of clinical conditions such as genital herpes caused by the herpes simplex virus, or chicken pox or shingles, caused by the varicella zoster virus.
In the treatment of certain conditions, it may be necessary to administer acyclovir to the patient in relatively large dosages to achieve the effective therapeutic levels of drug in the plasma, particularly when oral administration is desired. For example, in the treatment of shingles, it is recommended to administer acyclovir at a dosage regime of 800 mg five times per day. A tablet formulation containing 800 mg of acyclovir is currently available but its relatively large size sometimes renders it difficult to swallow by elderly patients, such patients being particularly susceptible to shingles.
We have now been able to prepare water-dispersible tablets containing acyclovir which can readily be dispersed in water to form a dispersion which can easily and conveniently be drunk by e.g. an elderly patient. More particularly the tablets of the invention meet the criteria for dispersible tablets set out in the British Pharmacopoeia (B.P. 1988, page 895, volume II) in that they disperse in water within 3 minutes to form a dispersion that will pass through a 710 .mu.m sieve.
Furthermore, at a high drug loading, the overall size of a tablet containing 800 mg acyclovir (for shingles) is still small enough to swallow. The patient, depending on his capability, thus has the choice of swallowing or dispersing the tablet.